Moving picture sound head



June 15, 1937. .1. N. EHRMEYER v MOVING PICTURE SOUND HEAD Filed June12, 1933 2 Sheets-Sheet l e e W IE N n M Patented June 15, 1937 PATENTOFFICE MOVING PICTURE SOUND HEAD John N. Ehrmeyer, Chicago, 111.

Application June 12, 1933, Serial No. 675,353

12 Claims.

This invention relates to sound heads and more particularly to motionpicture sound producing means, although certain features thereof may beemployed with equal advantage for other purposes.

It contemplates more especially the provision of a novel sound headwhich is simple, compact, and avoids the undesirable features ofimparting tension to the film as well as film flutter.

The intermittent sprocket and the sound sprocket are the most importantsprockets in the projector and sound head film drive. The intermittentsprocket is used to pull the film through the picture gate,intermittently stopping each successive picture frame accurately in thepicture aperture and in the same relative position as the precedingframe. Certainly if the sprocket is eccentric or if the teeth are wornor not spaced uniformly around the circumference of the sprocket, itwill be impossible to fulfill the above conditions. It may be repeatedthat the tolerances of eccentricity and tooth pitch must be held withinvery close limits, since any variations or inaccuracies will bemagnified on the screen in an amount equal to the degree ofmagnification of the projected picture.

The sound sprocket is used to pull the film through the sound gate at aconstant or uniform speed. As in the case of the intermittent sprocket,very close tolerances must be maintained since any variations willresult in a varying film speed which introduces distortion in soundreproduction. This distortion can be recognized as a harsh or raspysound noticed particularly on higher frequency notes produced by suchinstruments as the piccolo, fiute or violin. It might also be pointedout here that even though the proper tolerances may have beenmaintained, poor or distorted sound will result if the 49 sprockets havenot been designed properly or if sprockets are not used for the purposefor which they were intended.

The sound sprockets will be considered under actual operating conditionsfor the following 45 three cases, viz.: (l) in which the sound sprockettooth pitch is equal to the sprocket hole pitch as shown in Figure 1;(2) in which the tooth pitch is greater than the sprocket hole pitch;and

- (3) in which the tooth pitch is less than the sprocket hole pitch. Itis to be noted that the first condition represents an ideal case inwhich the sprocket hole pitch is equal to the tooth pitch. Also, it isto be recognized that each sprocket hole is engaged with a tooth andshould share its equal portion of the load.

For a condition of this sort it is necessary to have a sprocket diameteror sprocket tooth pitch which corresponds and equals the sprocket holepitch. With this condition fulfilled it will be found that the sprocketwill at least theoretically impart uniform filmv speed; however, it willbe found that in practice this ideal condition does not exist. It iscommon knowledge that film shrinks a certain amount depending upon itsage, use, and the treatment it has received. This, of course, wouldindicate that, in general, no two reels of film have shrunk an equalamount; therefore, the ideal case does not exist. In selecting asprocket to be used as a sound sprocket, it is necessary that its toothpitch be equal to and correspond to the tooth pitch of new or unshrunkfilm. If this is done, the tooth pitch will be greater than the sprockethole pitch when the sprocket is used with shrunken film. While thiscondition is not ideal, it is the condition under which all known feedsprockets must operate to produce the best available results underpresent limitations of devices of known design.

It is found, however, that the great tension which is thus placed on thefilm aggravates the flutter introduced by the, sprocket teeth and isfurther responsible for film mutilation. This has been largely orentirely overcome by subjecting the film to the least possible tensioncompatible with the necessity for keeping the film in focus at the gateor in the reunion of the light beam. While it has been impossible, or atleast impracticable up to the present time, to have the film pass overthe Movietone sprocket at a uniform rate of speed, a sprocket has beenproduced that will impart to the film as nearly a constant speed as ispossible or necessary within practical requirements and, further, a loophas been provided between this sprocket and the point from which thefilm leaves the projector, thereby avoiding or at least removing allundesirable metallic harmonics. The sound is taken off at the high pointof the sprocket where the film moves at a similar speed; therefore, thefilm moves past the light very nearly at a uniform rate of speed. Filmdisturbances, distortion, shake, flutter, undesirable metallicharmonics, film tension, and all heretofore uncontrollable variations,are either avoided or reduced to a negligible degree within practicalrequirements. 1

Nevertheless, with all known improvements, there still remains much tobe accomplished in producing substantially perfect moving picture filmand sound projection within practical requirements. Tension on the filmeither in the projection or sound head is very undesirable as it isresponsible for film mutilation and undue wear.

One object of the present invention is to simplify the construction andimprove the operation of the device of the character mentioned.

Another object is to provide a sound head which is simple, compact andinexpensive in construction.

Still another object is to provide a sound projector which is productiveof more perfect sound projection in synchronized relation with motionpicture film projection.

A further object is to provide a sound head having a film feedingsprocket presenting a round surface from which sound may be taken at apoint moving in synchronism and at a similar speed with the film.

A still further object is to provide a sound head having a film feedingsprocket which conforms with the variations in the film so as to effectthe feeding thereof without distortion, tension, or film disturbances.

Still a further object is to provide a sound head involving a filmfeeding sprocket and a shoe which is applied thereagainst merely to holdthe film in focus along the high point of the curved surface presentedby the sprocket which moves in synchronism with the film.

Other objects and advantages will appear from the following descriptionof an illustrative embodiment of the present invention.

In the drawings:

Figure 1 is an enlarged fragmentary sectional view in elevation of asound head embodying features of the present invention, it being shownin conjunction with a part of the moving picture projector head toclarify the disclosure.

Figure 2 is a sectional view taken substantially along line IIII ofFigure 1.

Figure 3 is a sectional view taken substantially along line III-III ofFigure 1.

Figure 4 is an enlarged fragmentary viewof the sound head sprocket withparts thereof broken away to clarify the showing.

Figure 5 is a sectional view taken substantially along line VV of Figure4.

Figure 6 is a fragmentary plan view of a motion picture film section.

The structure selected for illustration comprises a frame or casing I!)which is shown in association with a moving picture projection head llhaving film feeding instrumentalities more particularly described in theco-pending application serially numbered 671,648 and filed May 18, 1933.The moving picture projection head II is in communication with a firetrap I2 detachably connected therewith. A fire trap casing I3 issimilarly in communication with the moving picture projection head Ill,and a film l4 traverses therethrough in a manner more fully described inthe adjacent co-pending application which contains a full disclosure ofthe actuating instrumentalities and describes the synchronized operationthereof. In the moving picture film projection head H, a pair of studshafts l5 and I6 are journalled for projection into the film housing I!constituting a lateral extension of a casing [8 which has all of theactuating instrumentalities confined therein.

The stud shafts I5 and iii are intermittently driven to impartcorresponding rotation to film sprockets l9 and 2!], respectively, sothat one is just slightly in advance of the other to maintain the film[4 almost taut therebetween. As

shown, the sprockets l9 and 20 are disposed on either side of a lightprojecting aperture 2| corresponding substantially in size with a singleframe of the continuous moving picture film l4 having the usual linearseries of sprocket engaging apertures 22 and 23 proximate to the edgesthereof. Consequently, the film is maintained taut over the lightprojecting aperture to procure the proper focus with the aid of the filmgate 24 of arcuate configuration disposed in the path of the film l4 sothat the central aperture 25 therein will coincide and align with thefilm projecting aperture 2|, the gate 24 having a guide bar 26 formedthereon for slidable association in a correspondingly formed grooveprovided in the casing wall I8. As shown, the gate 24 is provided withpins 2! and 28 extending therefrom to impinge against threaded studs 29and 30 carried by lugs 3| and 32, respectively. The lugs 3i and 32extend from the casing I I, and spiral springs 33 envelop the pins 27and 28 so as to yieldingly urge the film gate 24 in the direction of thefilm M.

The film gate 24 is displaced to its operative position or removedtherefrom by virtue of a cam lever 34 mounted in the apertured extremity35 of the film gate bar 26 so as to be directed in the path of a stud 36adjustably mounted or anchored in an adjacent bracket. With thisarrangement, the film gate 24 may be retracted so as to afford filmlacing and unlacing preparatory or subsequent to film projection. Asshown, a shoe 31 has an enlarged fiat lateral extension 38 correspondingin shape and somewhat larger than the film gate aperture 25, it beingprovided with a correspondingly shaped aperture 39 for alignmenttherewith. The contacting surfaces of the shoe extremity 38 are providedwith upraised longitudinal edges based to correspond with the raisededges of the film gate 24 so as to abut thereagainst with the film l4therebetween so as to hold the latter in accurate focus.

The shoe 3'! is reciprocally guided relative to the film gate 24 and italternates in intermittent cooperation with the advancement of thesprockets l9 and 2|] so as to allow the advances of the film l4 withoutstress or obstruction thereto. A series of lenses are mounted in tubularcasings which are disposed between the light source and the projectingaperture 2| provided in the film housing H. In this instance, a tubularlens casing 40 extends within the film housing I"! between the lightprojecting aperture 2| in the front surface thereof and the shoeextremity 38, there being a sufficient clearance to permit thereciprocation of the latter in alternation with the intermittent advanceof the feeding sprockets l9 and 2E constituting a film driving meanstherefor. Another tubular light directing casing 4! extends from therearward side of the film gate 24 to a shutter housing (not shown) fortelescopic communication therewith so as to direct the rays emanatingfrom an arc lamp or other high powered light source which furnishes thenecessary medium for moving picture film projection. To effect soundproduction, an exciter lamp 42 is mounted in a socket 43 supported bythe bottom of the casing H) for emanating light through a lens 44carried by a tubular casing 45 which confronts a sound sprocket 45mounted on a stub shaft 41. The stub shaft 47 is horizontally journalledin spaced bearings 48 which are supported by brackets 49 integrally orotherwise joined to the wall of the casing H3. The stub shaft 4'! has aworm wheel 50 fixed thereon ltl to mesh with a worm 53 carried by ashaft 52 so as to impart continuous rotation to the stub shaft extension58 journalled in a bearing plate 53 fixed to the cover plate 54 of thecasing It) by means of; fasteners 55. The stub shaft extension 46 has areduced extremity 48" which receives the hub of the soundsprocket wheel46 disposed in the casing Iii in alignment with the film sprockets l3and 2!! fixed to the stud shafts l5 and I6, respectively.

While the sound head sprocket 46 is driven continuously, the filmsprockets I9 and 2B are intermittently driven through and by resort toinstrumentalities more particularly shown in the adjacent co-pendingpatent application so that one is just slightly in advance of the otherto maintain the film l4 almost taut between the sprockets l9 and 2%which are disposed on either side of the light projecting aperture 2|corresponding substantially in size with a single frame of thecontinuously driven moving picture film 14 having the usual linearseries of sprocket engaging apertures 22 and 23 proximate to the edgesthereof. Consequently, the film is maintained taut while in the path ofthe light projecting aperture 2i to procure the proper focus with theaid of the film gate 24 and shoe 3?.

In order to synchronize sound with the projection of pictures, the filmM is provided with any suitable sound registering indicia such as alinear series of transverse slits of varying light emanating intensitieswhich are formed therein to define a sound track, in this instanceadjacent to the linear series of sprocketengaging apertures 23; however,the character and position thereof may be varied within a wide range ascommercial practice may dictate. To effect the uniform application ofthe film l4 over the sound sprocket 46, the latter is provided withsprocket teeth 56 which are loosely associated therewith in a manner tobe more fully hereinafter described so as to conform with theirregularity in the film perforations 22. In consequence thereof, thefilm I4 is positively meshed therewith for effecting the traversethereover in synchronism with the movement thereof past the lightprojecting apertureQl.

A retractable shoe 5'! has an arcuate face 58 conforming in curvaturewith the sprocket 46 for cooperation in confronting relation therewithso as to uniformly apply the film l4 thereover. The film It has a linearseries of light slits 59 or sound track 59 provided thereon to projectbeyond the edge of the film sprocket? 46 so as to be in the path of thelight emanated from the exciter lamp i2 and received by a photo-electriccell 89. The photo-electric cell 60 is, in this instance, horizontallydisposed for mounting in a socket 6i provided in the side wall of thesound casing [B so that the terminals 62 thereof will projecttherethrough for connection to the loud speaker and amplified units (notshown). It is to be noted that the photo-electric cell 66 ishorizontally supported so that. the longitudinal axis thereof will be inparallelism with the axis of the sprocket 46 for extension within theconfines of the sprocket periphery so as to be in alignment with theexciter lamp $2., there beingan opaque screen or plate 63 disposedtherebetween with a light beam projecting aperture 64 directly in linewith the lens 44 disposed in the path of both the exciter lamp 42 andphoto-electric cell 50.

The screen 63 is, in this instance, formed integral with the retractableshoe 5! and conforms in curvature with the shoe face 58,.it being a'lateral extension thereof. To this end, the plate.

63 ,has the light beam projecting aperture 64 thereof located, so thatthe linear series of light emanating slits or film sound track 59 willtravel in the path thereof. The light emanating from the exciter lamp 42will, therefore, project through the aperture 64 for direction to thephoto-electric cell 59, thereby causing the latter to convert thesevariations in light impulses into sound production at uniform speeddetermined by the linear movement of the film l4.

To enable the yielding application of the shoe 5'! to the periphery ofthe sound sprocket 46 or effect the retraction therefrom, the shoe plate65 is provided with a plurality of elongated sockets 66 adjacent thetopand bottom edges thereof,- in this instance four, to cooperate withthreaded studs 61 projecting therethrough for anchored engagement withbrackets 68 carried by the bearing plate53, thereby guiding thereciprocal movement of the shoe 5? in confronting relation with thesprocket 45. The shoe plate 65 has upstanding lugs 69 extendingtherefrom for supporting pins H! which impinge against threaded studs Hand '12 carried by the lugs 13. The lugs 13 extend from the bearingplate 53 for projection through openings 14 provided in the shoe plate65, and spiral springs l5 envelop the pins IE! to impinge against thestuds H and 52 so as to yieldingly urge the shoe 5! in the direction ofthe film M in meshing engagement with the sound sprocket 46.

The shoe 5! is displaced in its operative position or removed therefromby virtue of a cam lever 16 mounted in the apertures boss ll of the shoeplate 65 so as to be directed in the path of a stud l8 adjustablymounted or anchored in a bracket l9 integrally or otherwise formed forextension from the bearing plat-e 53. With this arrangement, the soundsprocket shoe 5? may be retracted so as to afford film lacing orunlacing preparatory or subsequent to motion picture film and soundprojection. It is to be noted that the shoe 51 has upstanding edgesextending from the arcuate shoe surface 58 for the reception of the filmengaging teeth 5%; associated with the periphery of the sound sprocketit. In order that the sprocket teeth 56 may conform with and serve as anaccurate complement to the film apertures 22, they are movably anddetachably associated with the sprocket 56. teeth 58 are provided with acylindrical shoulder 81 which terminates in an enlarged circularbase'82.

' In order to afford the detachable association of the teeth 56 to thesound sprocket 46, the latter is provided with an annular groove 83provided in the side surface thereof. A circumferentially spaced seriesof circularapertures 84 are provided through the periphery 85 of thesound sprocket 46 proximate to the edge thereof for communication withthe annular groove 83. It is to be not-ed that the circumferentiallyspaced series of apertures 84 correspond substantially to the linearspaced series of apertures 22 provided on the film l4, and the diametersthereof are slightly greater than the diametral extent of the sprocketteeth shoulders 8! which are confined therein to afford a slightcircumferential movement and play. The sprocket teeth 56 project throughthe surface 85 of the sound sprocket 4% so that the base 82 thereof willengage theside surface 86 of the annular groove 83. The teeth 56 aresupported in their extended position by means of a circular ring 81which serves as a complement to the annular groove 33-, and has a Tothis end, the

groove 88 provided on the exterior peripheral edge thereof so as topresent a shoulder 89 for the engagement of the sprocket teeth base 82,thereby rendering them in position.

5 With this arrangement, the sprocket teeth 56 have the circular bases86 thereof resting on the grooved surface 88 of the retaining ring 81 toafford movement of the teeth 56 within the limits of the apertures 84which are somewhat larger in 40 diameter than the teeth shanks orshoulder 8|.

The retaining ring 81 of the sprocket 46 is detachably connectedtherewith for lodgment in the annular groove 83 by virtue of anysuitable fastening expedients such as threaded studs 99 1.5 inengagement with the side surface of the sound sprocket 46 so that thehead thereof will overlap the annular groove 83 therein to engage theretaining ring 81. This affords replacement of the teeth 56 and alsoprovides for cleansing as well as such other adjustments which maybecome necessary with the continued use thereof. It will be apparent,therefore, that the sound head sprocket teeth 56 will be self-displacingto conform with the variations in the size and spacing of the linearseries of film apertures 22, thereby avoiding or minimizing tension onthe film M as well as precluding the mutilation thereof. If desired,light projecting guide or screen 92 is mounted on the Wall of the casingII] as at 93 so as to present a light aperture guide 94 in directalignment with the film sound track 59 so as to confine the lightimpulses thereto and direct such to the adjacent photo-electric cell 69.

A felt pad 95 is preferably mounted on a bracket 96 secured to the wallof the casing ID as at 91 to confront the interior peripheral surface ofthe open film feeding or sound sprocket 46 to deaden the noise, minimizethe vibrations, preclude the transmission thereof to the photo-electriccell 66,

and to serve as a brake for the sprocket 46. As

shown, the film I4 is laced for meshing engagement with theintermittently rotating sprockets I9 and 29 and emerges from the filmhousing I! to present a loop 9| prior to engaging the sprocket teeth 56detachably associated with the sound sprocket 46. This precludes ordeadens all noise that may exist and precludes the development ofmetallic harmonics within the sound head or casing ill. The insertibleand movably associated sprocket teeth 56 conform with the variations inthe film |4 due to shrinkage and sprocket hole or aperture variations,thereby engaging the film |4 so as to move it through the sound head inthe path of the light rays Without mutilation, distortion, or other filmdisturbances. These variations in the film 4 heretofore precluded theapplication of the film l4 for movement over a large sprocket which hasvery accentuated advantages as is apparent from this preferreddisclosure. The

60 sprocket teeth 56 have the tendency to align quietly into positionfor meshing engagement with the film M to avoid distortion of sound,film shatter, friction and flutter.

It is apparent, therefore, that the film disturbances and distortionsare reduced to a negligible degree when the film 9| hits or firstcontacts the surface of the sound sprocket 46 when engaging the firsttooth 56 thereof in advance of the aperture opening 64 which presents ahigh point on the peripheral surface of the sound sprocket 46 movingsimultaneously and in synchronism with the film. At the high point onthe surface of the sprocket 46, the sound is taken so as to insureuniform film speed and synchronized sound production. All theseadvantages are attained without resort to a multiple of sprockets andpulleys and entirely devoid of tension on the film l4. Such advantagesattendant with the simplification in structure as well as a compactarrangement is productive of substantially perfect results in soundproduction synchronized with film projection.

So compact is the arrangement which is made possible by the novelinstrumentalities and combination thereof so that the distance betweenthe film projecting aperture 2| and the sound aperture 64 so as torequire only eight standard frames I4 50 the film l4 including the loop9| which may vary in extent depending upon the dictates of commercialpractice. In standard arrangements and assembly, there are no less thanfourteen film frames [4' between corresponding distances, and this is ofprimary significance as there is less possibility for noise such as filmloop slap where the distance is so small as eight film frames l4 apart.The closer the relation between the projected picture frame and theframe from which the sound is taken, the less possibility there is forinjury to the film as the latter is moving in a vertical direction so asto provide a tendency for side sway. The close relationship between theinstrumentalities so as to provide minimum distance between theprojector head aperture and sound head aperture, confines the path tosuch a limited extent as to preclude deviation in film traverse.

The edges of the film are in least contact with the mechanical partswith such an arrangement, and there is also little or no change in theheat or temperature from the projector aperture to the sound aperture,thereby rendering conditions more suitable to the longevity of the film.It is of further importance where there is a requirement for splicingthe film, since the extent of the part removed is much smaller than whenthe distances between the corresponding points as described supra aremore than eight frames apart. In fact, a compact arrangement which wouldafford a distance between corresponding points to be thirteen frames orless apart would be far more advantageous than known devices whichrequire a spacing in excess thereof. It is therefore of primaryimportance to note that applicants structure renders it possible to havethe projecting aperture and sound aperture eight or less frames apart torender this assembly far more compact and advantageous.

With the detachable and insertible teeth 56, the number thereof may bevaried as commercial practice may prescribe or dictate. For instancethere may be provided on the periphery of the sound sprocket 46, justenough teeth so that there will be one tooth 56 to the film frame M ormore for that matter depending upon particular conditions and operationwhich is more satisfactory as a dependent factor upon the number ofsprocket teeth engagement. The sound sprocket 46 may be composed ofbakelite in order to further minimize the noise or to render suchnegligible, and this is likewise true of the casing It! so as to deadenall noises and to preclude noise harmonics.

Various changes may be made in the embodiment of the invention hereinspecifically described without departing from or sacrificing any of theadvantages of the invention as defined in the appended claims.

I claim:

1. A moving picture sound head comprising a casing, a film feedingsprocket rotatably mounted in said casing, a moving picture film adaptedfor meshing engagement with said sprocket, said moving picture filmhaving an edge region thereof projecting beyond the peripheral surfaceof said sprocket, an arcuate shoe yieldingly mounted for contact withthe periphery of said sprocket to hold the film in engagement therewith,means comprising a lamp for directing light rays through the edge regionof said film, and a photo-electric cell in the path of said light rayspassing through said film for conversion to corresponding soundimpulses. I

2. A moving picture sound head comprising a casing, a film feedingsprocket rotatably mounted in said casing, said sprocket having a singleseries of ciroumferentially spaced teeth, a moving picture film adaptedfor meshing engagement with said sprocket teeth, said moving picturefilm having an edge region thereof projecting beyond the peripheralsurface of said sprocket, a shoe mount ed for resilientapplicationagainst the periphery of the sprocket with the filmtherebetween, means comprising a lamp for directing light rays throughthe edge region of said film, and a photo-electric cell in the path ofsaid light rays passing through said film for conversion tocorresponding sound impulses.

3. A moving picture sound head comprising a casing, a film feedingsprocket rotatably mounted in said casing, said sprocket having a singleseries of ciroumferentially spaced teeth, a moving picture film adaptedfor meshing engagement with said sprocket teeth, said moving picturefilm having an edge region thereof projecting beyond the peripheralsurface of said sprocket, a retractable shoe in yielding confrontingrelation with said sprocket for receiving the film therebetween, meanscomprising a lamp for directing light rays through the edge region ofsaid film, and a photo-electric cell in the path of said light rayspassing through said film for conversion to corresponding soundimpulses.

4. A moving picture sound head comprising a casing, a film feedingsprocket rotatably mounted in said casing, said sprocket having a singleseries of ciroumferentially spaced teeth, a moving picture film adaptedfor meshing engagement with said sprocket teeth, said moving picturefilm having an edge region thereof projecting beyond the peripheralsurface of said sprocket, a retractable shoe in yielding confrontingrelation with said sprocket for receiving the film therebetween, saidshoe having a lateral extension to cover the exposed edge region of saidfilm, there being a light projecting aperture in said shoe to coincidewith the exposed edge region of said film, means comprising a lamp fordirecting light rays through the edge region of said film, and aphoto-electric cell in the path of said light rays passing through saidfilm for conversion to corresponding sound impulses.

5. A moving picture sound head comprising a casing, a film feedingsprocket rotatably mounted in said casing, said sprocket having a singleseries of ciroumferentially spaced teeth, a moving picture film adaptedfor meshing engagement with said sprocket teeth, said moving picturefilm having an edge region thereof projecting beyond the peripheralsurface of said sprocket, a retractable shoe in yielding confrontingrelation with said sprocket for receiving the film therebetween, saidshoe having a lateral extension to cover the exposed edge region of saidfilm, there being a light projecting aperture in said shoe to coincidewith the exposed edge region of said film, means comprising a lamp fordirecting light rays through said shoe aperture and the edge region ofsaid film, and a photo-electric cell in the path of said light rayspassing through said film for conversion to corresponding soundimpulses.

6. A moving picture sound head comprising a casing, a film feedingsprocket rotatably mounted in said casing, said sprocket having a singleseries of ciroumferentially spaced teeth, a moving picture film adaptedfor meshing engagement with said sprocket teeth, said moving picturefilm having an edge region thereof projecting beyond the peripheralsurface of said sprocket, a retractable shoe in yielding confrontingrelation with said sprocket fcrreceiving the film therebetween, saidshoe having a lateral extension to cover the exposed edge region of saidfilm, there being a light projecting aperture in said shoe to coincidewith theexposed edge region of said film, said teeth being movablyassociated with the periphery of said sprocket to correspond withvariations in said film, means comprising a lamp for directing-lightrays through said shoe aperture and the edge region of said film, and aphoto-electric cell in the path of said light rays passing through saidfilm for conversion to corresponding sound impulses.

7. A moving picture sound head comprising a casing, a film feedingsprocket rotatably mounted in said casing, said sprocket having a singleseries of circumferentially spaced teeth, a moving picture film adaptedfor meshing engagement with, said sprocket teeth, said moving picturefilm having an edge region thereof projecting beyond the peripheralsurface of said sprocket, a retractable shoe in yielding confrontingrelation with said sprocket for receiving the film therebetween, saidshoe having a lateral extension to cover the exposed edge region of saidfilm, a member for retracting said shoe from said sprocket to affordlacing and unlacing of the film, said teeth being movably associatedwith the periphery of said sprocket to correspond with variations insaid film, means comprising a lamp for directing light rays through saidshoe aperture and the edge region of said film, and a photo-electriccell in the path of said light rays passing through said film forconversion to corresponding sound impulses.

8. A moving picture sound head comprising a casing, a film feedingsprocket rotatably mounted in said casing, said sprocket having a singleseries of ciroumferentially spaced teeth movably associated therewith, amoving picture film adapted for meshing engagement with said sprocketteeth, said moving picture film having an edge region thereof projectingbeyond the peripheral surface of said sprocket, a shoe reciprocablymounted relative to said sprocket to hold said film in contact with thesprocket periphery, means comprising a lamp for directing light raysthrough the edge region of said film, and a photo-electric cell in thepath of said light rays passing through said film for conversion tocorresponding sound impulses.

9. A moving picture sound head comprising a casing, a film feedingsprocket rotatably mounted in said casing, said sprocket having a singleseries of ciroumferentially spaced teeth, a moving picture film adaptedfor meshing engagement with said sprocket teeth, said moving picturefilm having an edge region thereof projecting beyond the peripheralsurface of said sprocket, a retractable shoe in yielding confrontingrelation with said sprocket for receiving the film therebetween, saidshoe having extending film contacting edges to afford the passage of thesprocket teeth without contact therewith, means comprising a lamp fordirecting light rays through the edge region of said film, and aphoto-electric cell in the path of said light rays passing through saidfilm for conversion to corresponding sound impulses.

10. A moving picture sound head comprising in combination a casing, afilm feeding member in the form of a drum rotatably mounted in saidcasing having a single series of circumferentially spaced teethprojecting outwardly adjacent to one end of the drum adapted byengagement with the apertures at one edge of a moving picture film tohold the film in position on the drum with the opposite edge portion ofthe film projecting beyond the end of the drum, an arcuate shoe pressedlightly inwardly toward the drum for holding a film lightly inengagement with the drum, means comprising a lamp for directing lightrays through the projecting edge portion of a film in position on thedrum, and means comprising a photo-electric cell in the path of thelightrays passing through said film for conversion to corresponding soundimpulses.

11. A moving picture sound head comprising in combination a casing, afilm feeding member in the form of a drum rotatably mounted in saidcasing having a single series of circumferentially' spaced teethprojecting outwardly adjacent to one end of the drum adapted byengagement with the apertures at one edge of a moving picture film tohold the film in position on the drum with the opposite edge portion ofthe film projecting beyond the end of the drum, an arcuate shoe pressedlightly inwardly toward the drum adapted by engagement with theprojecting edge portion of a film in position on the drum to cause saidprojecting portion to conform to the curvature of the correspondingportion of the film supported by the drum, means comprising a lamp fordirecting light rays through said projecting edge portion of the film,and means comprising a photo-electric cell in the path of the light rayspassing through said film for conversion to corresponding soundimpulses.

12. A moving picture sound head comprising in combination a casing, afilm feeding member in the form of a drum rotatably mounted in saidcasing having a single series of circumferentially spaced outwardlyprojecting teeth mounted thereon so as to have a limited amount of playwith respect to the drum at one end of the drum adapted by engagementwith the apertures at one edge of a moving picture film to hold the filmin position on the drum with the opposite edge portion of the filmprojecting beyond the end of the drum, an arcuate shoe pressed lightlyinwardly toward thedrum adapted by engagement with the projecting edgeportion of a film in position on the drum to cause said projectingportion to conform to the curvature of the corresponding portion of thefilm supported by the drum, means comprising a lamp for directing lightrays through said projecting edge portion of the film, and meanscomprising a photo-electric cell in the path of the light rays passingthrough said film for conversion to corresponding sound impulses.

JOHN N. EHRMEYER.

